Method of treating waste water and apparatus for treating waste water using the method

ABSTRACT

The present invention provides a method of treating waste water including nitrogen-containing organic compounds to convert harmless gases without post-treatment. The method comprises steps of spraying the waste water in a heated space to gasify the waste water to waste gas, and oxidizing the waste gas by contacting with a catalyst to convert the nitrogen-containing organic compound into harmless gases.  
     This application also discloses an apparatus for treating waste water using the method.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of treating waste water to convert nitrogen-containing organic compounds into harmless gases such as nitrogen gas, carbon dioxide and the like, and an apparatus for treating waste water using the method. In particular, the invention relates to a method for treating waste water exhausted from a semiconductor manufacturing plant after dissolving and washing a photoresist, and relates to an apparatus suitable for treating such a waste water.

[0003] 2. Prior Art

[0004] Waste water exhausted from various chemical plants, semiconductor manufacturing plants and the like sometimes includes nitrogen-containing organic compounds. Conventionally, as a method of treating waste water, an incineration method, a biological treatment method utilizing the function of micro-organisms, a decomposition treatment method utilizing supercritical water, and the like have been proposed.

[0005] The incineration method is the one in which waste water including nitrogen-containing organic compounds and/or hydrocarbons are burned at a high temperature so as to be oxidized, decomposed and treated, and nitrogen oxides (NO_(x)) are produced as a result. Exhausting nitrogen oxides to the atmosphere will cause acid rain, and thus it is necessary to prepare treatment facilities for converting NO_(x) to harmless compounds. Therefore, the treatment of waste water according to incineration methods has such a disadvantage that the treatment facilities are apt to be enlarged and require higher construction cost.

[0006] The biological treatment method utilizes micro-organisms for decomposing organic compounds such as a nitrogen-containing organic compound in waste water into nitrogen, water and carbon dioxide. This method has an advantageous effect that organic compounds can be treated under moderate conditions and converted into harmless nitrogen gas and the like through decomposition thereof. However, this method has a disadvantage that the efficiency of decomposition is low, and we can not help enlarging the scale of the apparatus in order to guarantee the sufficient ability to treat waste water. Large treatment facilities cause the higher cost for construction of them, similarly to the incineration method. Furthermore, the biological treatment method requires post-treatment of excess sludge produced through decomposition of organic compounds. Thus, the biological treatment method has some problems.

[0007] The decomposition treatment method utilizing supercritical water is the one which utilizes the physical and/or chemical properties of water in a supercritical state. In order to render water supercritical, it is necessary to maintain water into a state of high temperature and high pressure. Thus, heat resistance and pressure tightness are strictly required for treatment facilities, and devices such as a high pressure pump and a high pressure compressor are needed in order to accomplish the supercritical state. Furthermore, when organic compounds included in waste water is low in concentration, it is necessary to concentrate waste water prior to decomposition treatment with supercritical water.

[0008] Recently, a method which comprises steps of gasifying waste water to produce waste gas and oxidizing and decomposing the waste gas with a catalyst is suggested as a method of treating waste water without requiring large facilities and higher construction cost.

[0009] For example, Japanese Patent unexamined laid-Open No.83081/90 (hereinafter referred to as the prior art “1”) discloses a method of concentrating waste water through evaporating water therein, and then separating a non-volatile contaminant and a vapor in the concentrated waste water, and oxidizing the vapor with a catalyst in the presence of water vapor. In this method, the step of evaporation is carried out at a temperature of about 82° C. to about 170° C., and silica, alumina or chromic oxide is used as a catalyst. Therefore harmful gases such as NO_(x) and SO_(x) are produced by catalytic oxidation and require facilities for post-treating the oxidized products.

[0010] Furthermore, Japanese Patent unexamined laid-open No.75913/97 (hereinafter referred to as the prior art “2”) discloses a method of treating photographic processing waste water. In the method, waste water is heated by microwave and a residual solid material is separated and removed, and thereafter, ammonia, which is included in a vaporized gas, is converted into nitrogen gas and water. The nitrogen gas can be exhausted in the atmosphere as it is, and the treated water can be drained into a sewerage system. In such method, harmful NO_(x) and SO_(x) are not produced as a resulting product, and thus it is not necessary to provide post-treatment facilities for the resulting product with the apparatus of treating waste water. However, the prior art “2” does not disclose a catalyst with which ammonia gas is decomposed into nitrogen gas and water vapor. Thus, the method disclosed in the prior art “2” can not be directly applied to waste water including nitrogen compounds other than ammonia, particularly, waste water exhausted from a semiconductor manufacturing plant after cleaning photoresist. This is because the waste water includes nitrogen-containing organic compounds such as tetramethylammonium hydroxide, which is difficult to be gasified by microwaves.

SUMMARY OF THE INVENTION

[0011] The present invention has been carried out in view of these circumstances, and it is an object of the invention to provide a method of treating waste water including nitrogen compounds other than ammonia, in particular, nitrogen-containing organic compounds to convert the nitrogen-containing organic compounds into harmless gases such as nitrogen gas and carbon dioxide, without post-treatment. Another object of the present invention is to provide an apparatus for treating waste water using the inventive method of treating waste water.

[0012] One aspect of the present invention is a method of treating waste water which comprises a first step of spraying waste water including a nitrogen-containing organic compound in a heated space to gasify substantially all amount of the waste water to waste gas; and a second step of oxidizing the waste gas by contacting with a catalyst to convert the nitrogen-containing organic compound into nitrogen gas, carbon dioxide and water vapor.

[0013] Another aspect of the present invention is an apparatus for treatingwastewaterwhich comprises ameans for gasifying waste water, which includes a sprayer for spraying waste water; a gasifying area into which waste water is introduced, and in which the waste water is gasified by the gasifying means to produce waste gas from the waste waster; and a reaction area which contains a catalyst for oxidizing the waste gas delivered from the gasifying area, and from which an oxidized gas is exhausted.

BRIEF DESCRIPTION OF DRAWINGS

[0014] FIGS. 1 to 3 show a first to a third embodiments of an apparatus of the present invention respectively.

[0015] In these Figures, the inventive apparatus comprises a sprayer (7) as a means for gasifying waste water, a gasifying area (10,10′), a reaction area (20) containing a catalyst (22), and a line (11) connecting the gasifying area (10,10′) to the reaction area (20).

DETAILED DESCRIPTION OF THE INVENTION

[0016] [Method of Treating Waste Water]

[0017] The method of treating waste water of the present invention comprises the steps of: spraying waste water into a heated space to gasify substantially all amount of the waste water to waste gas (the step is referred to as “gasifying process”); and oxidizing the waste gas by contacting with a catalyst (the step is referred to as “catalytic oxidation process”).

[0018] The waste water to be treated according to the method of the present invention includes nitrogen-containing organic compounds. Any nitrogen-containing organic compound soluble in water may be included in the waste water. Specific examples of nitrogen-containing organic compounds include amines such as methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine and ethylendiamine; imines such as ethyleneimine; nitrils such as acetonitrile and acrylonitrile; amides such as acetamide; quaternary alkylammonium salts such as tetramethylammonium hydroxide, tetraethylammonium hydroxide and choline; alkanolamine such as monoethanolamine and diethanolamine; and the like.

[0019] The amount of nitrogen-containing organic compounds in the waste water does not matter. When the concentration of nitrogen-containing organic compound included in waste gas provided by spraying waste water into a heated space to gasify substantially all amount of waste water is excessively increased, there may occur the problem associated with excessive increase of a calorific value upon catalytic oxidation. However, the problem can be solved by increasing the amount of oxygen or air as provided for catalytic oxidation.

[0020] Not only the nitrogen-containing organic compounds but also nitrogen-free organic compounds, particularly hydrocarbons may be included in the waste water. As for developer waste water exhausted from a semiconductor manufacturing plant, hydrocarbons which are dissolved from a resin as a resist material is contained in the developer waste water.

[0021] The heated space, where the substantially all amount of waste water to be treated is gasified, is specifically heated under normal pressure to 100° C. or more, preferably to 250° C. or more, more preferably to 500° C. or more. The sprayed waste water is heated up to such a temperature that water as well as organic compounds included in the waste water can be gasified in the heated space. Even if a less volatile and high molecular organic compound is included in the waste water, such an organic compound can be decomposed and gasified by heating the same to 500° C. or more. Tetramethylammonium hydroxide, which is included in developer waste water exhausted from a semiconductor manufacture, is decomposed into trimethylamine and methanol at about 130° C. and gasified.

[0022] Incidentally, upper limitation of the temperature in the heated space is 700° C. or less, preferably 550° C. or less, because heating the waste water at a temperature of over 700° C. is disadvantageous in view of fuel for heat.

[0023] As a means for heating the sprayed waste water in the heated space, a heater is most commonly used. The waste water could be easily gasified by spraying it into a closed vessel under a condition having a high temperature and reduced pressure. Furthermore, the sprayed waste water could be gasified by contacting it with another gas heated to a higher temperature in a heated space. Oxygen or air used for oxidation in the following catalytic oxidation process may be used as the heated gas used for gasifying the waste water. A treated gas discharged after the catalytic oxidation process is also usable, because the treated gas is sometimes elevated in a higher temperature by exothermic reaction at the gasifying process and the oxidation reaction.

[0024] The catalytic oxidation process is carried out by bringing the waste gas together with oxidant such as oxygen and air into contact with a catalyst.

[0025] A catalyst for the catalytic oxidation process comprises an oxide (hereinafter referred to as the component “A”) comprising titania and/or titania-silica; an oxide (hereinafter referred to as the component “B”) of at least one element selected from the group consisting of vanadium, tungsten, molybdenum, cerium and iron; and a metal or an oxide thereof (hereinafter referred to as the component “C”) of at least one element selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, manganese, chromium and copper.

[0026] A preferred catalyst is the one in which the content of the component “A” is 70% to 99% by mass, the content of the component “B” is 0.5% to 30% by mass, and the content of the component “C” is 0.001% to 20% by mass, based on the total mass of catalyst.

[0027] The component “A” in the catalyst improves activity and durability of the catalyst. The catalyst containing the component “A” of less than 70% by mass therein shows insufficient activity and durability. On the other hand, the catalyst containing the component “A” of more than 99% by mass therein shows insufficient activity due to relatively decreasing the contents of both components “B” and “C”. The component “A” is preferably included in the catalyst in the form of a composite oxide such as titania-silica, because the morphology of titania-silica is superior to that of single component oxide titania in activity and durability. For example, Kozo Tanabe (CATALYST, vol.17, No.3, page 72, 1975) teaches that a binary composite oxide consisting of Ti and Si, which is well known to a composite oxide presenting solid acid, shows more remarkable acid properties comparing with a single oxide of each of the constituent elements. Furthermore, it is known that titania-silica has an amorphous or amorphous-like fine structure, and thereby has a high surface area and a large pore volume. The reasons why the composite oxide (titania-silica) is excellent in catalyst performance are not exactly known. However, it is considered as follows: an improvement in a basic gas adsorbing performance, the tendency of the components “B” and “C” to highly disperse, and the like would be realized by specific properties as mentioned above, and thus the catalyst containing titania-silica can be superior to the catalyst consisting of titania in catalytic activity.

[0028] The component “B” improves selectivity of the catalyst. The catalyst containing the component “B” of less than 0.5% by mass shows insufficient selectivity, while the catalyst containing the component “B” of more than 30% by mass often shows insufficient activity.

[0029] The component “C” preferably comprises at least one metal selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, chromium, manganese and copper, or an oxide thereof in a total amount of 0.001% to 20% by mass. Furthermore, the component “C” can be divided broadly into the group “C1” consisting of platinum, palladium, iridium, rhodium and ruthenium, and the group “C2” consisting of chromium, manganese and copper. Although a component belonging to the group “C1” has higher activity than the one belonging to the group “C2”, the catalyst containing the component “C1” in an amount of more than 10% by mass does not improve its activity as expected regardless of higher cost. Therefore, when the component “C1” is used alone as the component “C”, the preferable content of the component C1 is in the range of 0.001% to 10% by mass based on the total mass of catalyst. On the other hand, a component “C2” has lower activity than a component “C1”, and thus the component “C2” is preferably included in an amount of 1.0% by mass or more in order that the catalyst provides sufficient activity. Therefore, when the component “C2” is used alone as the component “C”, the preferable content of the component “C2” is in the range of 1.0% to 20% by mass based on the total mass of catalyst.

[0030] These catalysts may be used in the form of a proper molded shape, or may be supported with a carrier.

[0031] The catalytic oxidation process is carried out by providing gasified waste water (i.e. waste gas) together with oxidant such as oxygen or air in a reaction area containing the catalyst mentioned above. The inlet temperature of the reaction area is preferably controlled in the range of 100 to 400° C. The reaction space having a temperature of less than 100° C. at the inlet cannot provide such sufficient oxidation efficiency with the result that some unoxidized organic compound remains. On the other hand, where the reaction space is controlled at a temperature of more than 400° C., a nitrogen-containing compound is excessively oxidized to produce nitrogen oxides (NO_(x)) easily, and thus post-treatment of the resultant NO_(x) is needed. Indeed, when a mixture of waste gas and oxidant which are fed to the catalytic oxidation process has a temperature ranging of 100° C. to 400° C., the mixture can be introduced into the reaction area as it is, while when the temperature of the mixture to be fed to the catalytic oxidation process is lower than the one adjusted in the reaction area, the mixture should be re-heated and then be introduced into the reaction area.

[0032] According to the preferred embodiment of the present invention, the waste gas flows at a space velocity (SV) of 500 to 50000 per hour at a temperature of 100° C. to 400° C. More preferable space velocity is in the range of 1000 to 10000 per hour. The space velocity (SV) of less than 500 per hour requires a large amount of catalyst and a larger apparatus for treating waste water with a result in unsatisfied efficiency, while the SV of more than 50000 per hour remarkably decreases the efficiency of decomposing nitrogen-containing organic compounds.

[0033] The waste gas discharged after the gasifying process is oxidized and decomposed in the catalytic oxidation process under the above-mentioned conditions to be converted into harmless gases such as nitrogen gas, carbon dioxide and water vapor. These harmless gases may be exhausted into the atmosphere as they are.

[0034] Besides nitrogen-containing organic compound and hydrocarbon, waste water to be treated sometimes includes a metal element (for example, Si), sulfur, and/or an organic compound which is difficult to decompose (for example, rubber or a thermosetting resin). Such a metal element, sulfur and/or a hardly decomposable organic compound cannot be gasified in the gasifying process and are remained as solid materials. The solid materials could give an undesired effect to the catalyst, and cause decrement of reaction efficiency in the catalytic oxidation process. Therefore, it is preferred to separate and remove such harmful solid materials from the waste gas, prior to transferring the waste gas from the gasifying process to the catalytic oxidation process.

[0035] The harmful solid materials are preferably removed with a pre-treating agent. Preferable examples of the pre-treating agent include at least one selected from the group consisting of alumina, silica, titania and zirconia. Such a pre-treating agent may be commonly used in the shape of pellet, but not limited thereto.

[0036] According to a method of treating waste water of the present invention, nitrogen-containing organic compounds including in waste water are selectively oxidized and decomposed so that the production of NO_(x) and/or ammonia can be inhibited, and thus it is not necessary to prepare facilities for post-treating NO_(x) and/or ammonia. Indeed, nitrogen component included in waste water is converted into harmless nitrogen gas, while carbon component is converted into carbon dioxide, and thus such resulting gases can be exhausted to the atmosphere as they are.

[0037] [Apparatus for Treating Waste Water]

[0038] The apparatus for treating waste water of the present invention uses the method of treating waste water mentioned above and comprises the following elements: a means for gasifying waste water, which includes a sprayer for spraying waste water; a gasifying area into which waste water is introduced, and in which the waste water is gasified by the gasifying means to produce waste gas; and a reaction area which contains a catalyst for oxidizing the waste gas delivered from the gasifying area, and from which an oxidized gas is exhausted. The apparatus in accordance with the invention may further comprise a pretreatment area for removing a solid material not gasified in the gasifying area.

[0039] The inventive apparatus will be explained referring to accompanying drawings. Incidentally, in the drawings, elements shown with the same numerals are identical or similar to each other, and thus the explanation about the elements will not be repeated.

[0040] A first embodiment of the inventive apparatus for treating waste water as shown in FIG. 1 employs the combination of a sprayer (7) and a heater (5) as a means for gasifying waste water in a substantially all amount.

[0041] A closed vessel (1) constitutes a gasifying area (10), and the heater (5) is equipped around the closed vessel (1). The sprayer (7), which constitutes the gasifying means with the heater (5), is set in the vessel (1). The waste water is fed with a pump to the sprayer (7) while air for spraying is fed with a blower to the sprayer (7), and mixture of the waste water and the air can be sprayed by the sprayer (7) to gasify the waste water to waste gas.

[0042] The closed vessel (1) has an inlet (2) through which air for oxidizing waste gas is introduced, and an outlet (4) through which the waste gas and the air for oxidation are discharged. The inlet (2) is provided on one side of the vessel (1) and the outlet (4) is provided on the opposite side thereof. The temperature in the closed vessel (1) is monitored with a temperature sensor provided therein, and the heater (5) is controlled by a temperature controller (3) so that the temperature in the closed vessel (1) can be maintained to a temperature sufficient for gasifying the waste water.

[0043] On the upstream side in the gas flow direction with respect to the outlet (4), a pre-treating agent (6) is set as a pre-treatment area.

[0044] A line (11) connects the gasifying area (10) to a reaction area (20).

[0045] The reaction area (20) comprises a closed vessel (21) containing the oxidation catalyst (22), wherein the waste gas delivered from the gasifying area (10) through an inlet (21a) of the reaction area (20), and an oxidized gas by contacting with the oxidation catalyst (22) are exhausted through an outlet (21b) of the reaction area (20). A second heater (24) (hereinafter referred to as a “reheater”) is provided on the gas supply line (11) between the outlet (4) and the inlet (21a), so that the waste gas can be heated prior to introducing into the reaction area (20) when the temperature of the gas discharged from the gasifying area (10) is excessively lowered. A temperature controller (23) having a temperature sensor is provided near the inlet (21a). The temperature controller (23) controls the temperature of the reaction area (20) so that the temperature of the introduced gas thereinto can be maintained to a temperature suitable for catalytic oxidation by switching on the reheater (24) when the introduced gas temperature is excessively lowered.

[0046] As the pre-treating agent (6), may be used any one of pre-treating agents exemplified in connection with the inventive method of treating waste water, namely, at least one selected from the group consisting of alumina, silica, titania and zirconia. As the catalyst (22), may be used any one of catalysts exemplified in connection with the inventive method of treatingwaste water, namely, a catalyst comprising the component “A” of an oxide comprising titania and/or titania-silica; the component “B” of an oxide of at least one metal selected from the group consisting of vanadium, tungsten, molybdenum, cerium and iron; and the component “C” of at least one metal selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, manganese, chromium and copper, or an oxide thereof.

[0047] In the apparatus for treating waste water of the present invention, waste water and air are supplied to the gasifying area (10) and sprayed and heated therein, and thus substantially all amount of the waste water is gasified to waste gas. Nonvolatile components such as Si, sulfur and/or a thermosetting resin component, namely solid material, which cannot be gasified in the gasifying area (10), are removed using a pre-treating agent. Then, a resulting waste gas after removing nonvolatile components from the waste gas is fed to the reaction area (20), in which the resulting waste gas is selectively oxidized by contacting with a catalyst to be converted into nitrogen gas, carbon dioxide and water vapor. Resultant gases such as nitrogen gas, carbon dioxide and water vapor can be exhausted from the reaction area (20) to the atmosphere as they are, because the resultant gases are harmless.

[0048] Incidentally, in the first embodiment of the inventive apparatus, the pre-treating agent may not be provided in the case that waste water to be treated includes little amount of nonvolatile components. Oxygen or air for oxidation may be fed into the reaction area (20) as well as the gasifying area (10).

[0049] Next, a second embodiment of the apparatus for treating waste water in accordance with the present invention will be explained on the basis of FIG. 2.

[0050] A closed vessel (1) constitutes a gasifying area (10′) and a sprayer (7) as a gasifying means is set in the vessel (1). Waste water to be treated is fed with a pump to the sprayer (7), while air for spraying is fed with a blower to the sprayer (7). The waste water and the air for spraying would be sprayed in the closed vessel (1) to gasify the waste water to waste gas. The closed vessel (1) has an inlet (2) one side thereof. Heated air by a heater (8) can be introduced into the vessel (1) through the inlet (2).

[0051] The temperature of the reaction area (20) is controlled with a temperature controller (23) by monitoring a temperature in the reaction area (20) with a temperature sensor provided near the inlet in the reaction area (20) and controlling the heater (8) in order to make the waste gas temperature sufficient for catalytic oxidation.

[0052] The reaction area (20) is identical to the one in the first embodiment of the inventive apparatus described above.

[0053] In the second embodiment of the apparatus for treating waste water, waste water to be treated and air for spraying are supplied to the sprayer (7), and are sprayed in the closed vessel (1) by the sprayer (7), while air heated with a heater (8) is supplied into the closed vessel (1). Waste water sprayed in the closed vessel (1) is mixed with the heated air, and thereby the sprayed waste water can be heated enough to gasify to waste gas. A mixture of the waste gas and the heated air from the vessel (1) is introduced into a reaction area (20), in which the mixture is selectively oxidized in contact with a catalyst (22), and thus nitrogen-containing organic compounds included in the waste gas are converted into nitrogen gas, carbon dioxide and water vapor. The resultant gases by oxidation can be exhausted from the reaction area (20).

[0054] According to the second embodiment of the inventive apparatus, the temperature control of the reaction area (20) is accomplished by the temperature controller (23) and the heater (8). Setting the heater (8) on the upstream in the gas flow direction with respect to the inlet (2) of the gasifying area (10′) enables to provide the simplified and compacted apparatus, and furthermore provide a simplified temperature control mechanism. In view of this, the second embodiment of the inventive apparatus is more advantageous than the first embodiment.

[0055] Next, a third embodiment of the apparatus for treating waste water of the present invention will be explained on the basis of FIG. 3.

[0056] In light of the fact that a treated gas exhausted from the reaction area (20) has a higher temperature than ordinary temperature in the second embodiment described above, the treated gas is utilized for heating air for oxidation introduced into the gasifying area (10′) in the third embodiment of the inventive apparatus. Therefore, a heat exchanger (9) is provided on air supply line between a blower for oxidant air and a heater (8). The treated gas delivered from the reaction area (20) and the oxidant air are introduced into the heat exchanger (9), where the oxidant air is heated by given a thermal energy from the treated gas having higher temperature. The heated air for oxidizing air is introduced from the exchanger (9) to the heater (8), and the treated gas having a lowered temperature may be exhausted to the atmosphere.

[0057] According to the third embodiment of the inventive apparatus, thermal energy of a treated gas discharged from the reaction area (20) can be effectively utilized, thereby an energy-saving can be achieved in the heater (8) for heating air for oxidation. This is an advantage of the third embodiment.

[0058] Incidentally, in the second and third embodiments of the inventive apparatus, if necessary, a pre-treating agent may be provided in the gasifying area (10). Furthermore, in each of the first to third embodiments, for the purpose of improving the efficiency of diffusion and/or mixing gases introduced in the gasifying area (10,10′), a wire-netting may be set in the closed vessel and/or the closed vessel may be filled with a lot of ring-shaped substrates.

[0059] As described above, an apparatus for treating waste water of the present invention does not require large facilities and high cost for construction because the apparatus substantially comprises two closed vessels, one constituting a gasifying area and the other constituting a reaction area.

EXAMPLE

[0060] [Preparation of Catalysts]

[0061] Catalyst “1”:

[0062] A composite oxide consisting of titania and silica was prepared according to the following procedure. 21.3 kg of SNOWTEC 20 (which is a silica sol manufactured by Nissan Chemical Industries, Ltd. and includes about 20% SiO₂ by mass) was added to 700 liters of 10% by mass of aqueous ammonia, and agitated and mixed therewith. 340 liters of a sulfuric acid solution of titanyl sulfate was slowly dropped to the resulting mixture while agitated, so as to provide a gel material. This gel material was left for three hours, and thereafter filtrated and water-washed, and dried at 150° C. for ten hours, and then calcined at 500° C. for six hours. The resulting powder had a composition of a molar ratio of TiO₂:SiO₂=4:1, and a BET specific surface area of 200 m²/g.

[0063] 12 kg of 15% monoethanolamine including 2.00 kg of ammonium metavanadate and 0.77 kg of ammonium paratungstate was added to 20 kg of the above powder, and starch as a molding assistant was added thereto, and mixed them by a kneader. The obtained mixture was formed into a honeycomb using an extruder, the honeycomb having an outside dimension of 80 square mm, a cell opening of 2.8 mm, a thickness of 0.5 mm and a length of 450 mm.

[0064] This honeycomb substrate was dried at 80° C., and calcined at 450° C. in an air atmosphere for five hours. The composition of the calcined honeycomb substrate had a mass ratio of Ti—Si composite oxide:V₂O₅:WO₃=90:7:3.

[0065] This honeycomb substrate was impregnated with an aqueous palladium nitrate solution, and dried at 150° C. for three hours, and calcined at 450° C. in an air atmosphere for three hours to produce a catalyst “1”. The catalyst “1” had a composition of mass ratio of Ti—Si composite oxide:V₂O₅:WO₃:Pd=89.1:6.9:3:1, a BET specific surface area of 120 m²/g and a pore volume of 0.45 cm³/g.

[0066] Catalyst “2”:

[0067] Catalyst “2” was prepared in the same manner as the catalyst “1”, except that a commercial titania powder (having a BET specific surface area of 30 m²/g) was used instead of a titania-silica powder. The obtained catalyst “2” had a composition of a mass ratio of TiO₂:V₂O₅:WO₃:Pd=89.1:6.9:3:1, a BET specific surface area of 22 m²/g and a pore volume of 0.24 cm³/g.

[0068] Catalyst “3”:

[0069] A powdered γ-alumina having a specific surface area of 150 m²/g was added to an aqueous oxalic acid solution so as to be slurried. A cordierite carrier in the form of a honeycomb (having an outside dimension of 150 square mm, a cell opening of 1.5 mm, a thickness of 0.35 mm and a length of 50 mm) was coated with the obtained slurry, dried and calcined to prepare a catalyst carrier. The content of Al₂O₃ was 15% by mass of the catalyst carrier. The catalyst carrier was impregnated with an aqueous solution including platinum nitrate, and dried at 100° C., and calcined at 450° C. in an air atmosphere for three hours so as to provide a platinum based catalyst. The content of platinum supported with the carrier was 0.1% by mass of the catalyst.

[0070] [Treatment of Waste Water]

EXAMPLE 1

[0071] In an apparatus as shown in FIG. 1, a closed vessel constituting a gasifying area was filled with 240 milliliters of rings made of SUS. Each of the rings has a diameter of 5 mm and a length of 6 mm. A reaction area contained 120 milliliters of the catalyst “1” prepared as mentioned above. An aqueous solution including tetramethylammonium hydroxide in 3% by mass was treated as a model of waste water under the following conditions.

[0072] The waste water was continuously supplied to the gasifying area at a supply speed of 2.7 g/min. with a pump, and sprayed by a sprayer, wherein air and air for spraying had been flowed at a flow rate of 2.6 liters/min. in a total amount under the standard state. The temperature of the gasifying area was set to a temperature of 300° C. using a heater controlled by a temperature controller. The temperature at an inlet of the reaction area was set to 275° C., 300° C. and 325° C., and the waste water was treated under the set conditions respectively. Treated gases under the respective conditions were discharged from the reaction area and the compositions of the treated gases were analyzed respectively. Incidentally, a space velocity in the reaction area corresponded to 2980 per hour.

[0073] The result of an analysis of the treated gases is shown in Table 1, in which the symbol “ND” represents—not detected—; “THC” represents the concentration of the total hydrocarbon left in a dried gas, calculated in terms of methane; and “TOC” represents the concentration of the total organic carbon included in acondensed liquid; and furthermore, “AMMONIA” represents the concentration of ammonia under the wet condition; and each of columns represents the concentration under the dried condition.

EXAMPLE 2

[0074] Example 2 was conducted in the same manner as Example 1, except that the catalyst “2” was used instead of the catalyst “1”. The composition of the treated gases was analyzed. The result is shown in Table 1.

COMPARATIVE EXAMPLE 1

[0075] Comparative Example 1 was conducted in the same manner as Example 1, except that a reactor contained the catalyst “3”, and the amount of the catalyst “3” was exchanged for 16 milliliters. Incidentally, the temperature of a reactor was set to 325° C.

[0076] The result of an analysis of the treated gases is shown in Table 1. TABLE 1 CATA- CATALYST 1 CATALYST 2 LYST 3 TEMPERA- 275° 300° 325° 275° 300° 325° 325° TURE C. C. C. C. C. C. C. TRIMETHYL- ND ND ND ND ND ND ND AMINE (ppm) METHANOL ND ND ND ND ND ND ND (ppm) THC (ppm) 4 3.5 3 4 4 3 15 TOC (mg/l) 11 13 18 17 14 15 12 AMMONIA 210 90 ND 350 160 0.7 0.9 (ppm) NO_(x) (ppm) ND 0.2 20-30 ND 1 30-40 350 N₂O (ppm) ND ND ND ND ND 10 150 CO (ppm) ND ND ND 2 ND ND 15 CO₂ (ppm) 3300 3400 3350 3350 3350 3400 3400

[0077] Tetramethylammonium hydroxide in waste water can be decomposed into trimethylamine and methanol at a temperature of about 130° C. In the case of using any one of the catalysts “1”, “2” and “3”, trimethylamine or methanol was not detected, and thereby it is found that trimethylamine and methanol were oxidized in the reaction area.

[0078] When the catalyst “3” was used, the concentration of each of NO_(x) and N₂O was higher, and thereby it is found that a nitrogen compound was converted into a nitrogen oxide. Furthermore, from the concentration of carbon dioxide, it is found that most of organic carbon was oxidized into carbon dioxide. On the other hand, when the catalyst “1” or “2” was used, carbon monoxide was little detected even at each of the temperatures. However, when the catalyst “3” was used, 15 ppm of carbon monoxide was detected.

[0079] Furthermore, in connection with nitrogen components, when the catalyst “1” or “2” was used, ammonia was detected at a temperature of 300° C. or less. However, when the catalyst “1” was used, ammonia was not detected at a temperature of 325° C., and when the catalyst “2” was used, 0.7 ppm of ammonia was detected at the temperature. Besides, when the catalyst “1” or “2” was used, NO_(x) was detected in a very small amount, and thus most of nitrogen component was converted into nitrogen gas.

EXAMPLE 3

[0080] In an apparatus for treating waste water as shown in FIG. 1, a gasifying area contained 60 milliliters of a spherical γ-alumina pellet having a diameter of 5 mm as a pre-treating agent, while a reaction area contained 28 milliliters of the catalyst “1”. Condensed waste water exhausted from a semiconductor products manufacturing plant was used, which has a composition as shown in Table 2.

[0081] The waste water was continuously supplied to the gasifying area at a supply speed of 0.4 g/min. with a pump, and sprayed by a sprayer, wherein air and air for spraying had been flowed at a flow rate of 2.0 liters/min. in a total amount under the standard state. The temperature of the gasifying area was set to a temperature of 300° C. using a heater controlled by a temperature controller. The temperature of the reaction area was set to 300° C., 325° C. and 350° C. The composition of treated gases was analyzed under respective temperatures. Incidentally, a space velocity in the reaction area corresponded to 5400 per hour.

[0082] The results of analyses of waste water before treatment and a treated gases discharged from a reacting area are shown in Table 2, in which the symbol “ND” represents—not detected—.

EXAMPLE 4

[0083] Example 4 was conducted in the same manner as Example 3, except that the catalyst “2” was used instead of the catalyst “1”. The composition of treated gases was analyzed. The result of an analysis thereof is shown in Table 2. TABLE 2 TREATED GAS TREATED GAS WASTE WATER (CATALYST 1) (CATALYST 2) TEMPERATURE (°C.) 300 325 350 300 325 350 TETRAMETHYL- 29100 — — — — — — AMMONIUM HYDROXIDE (mg/l) TOG (mg/l) 19200 77 30 29 210 36 31 Si (mg/l) 40 — — — — — — S (mg/l) 8 — — — — — — Al (mg/l) 1 — — — — — — TRIMETHYLAMINE (ppm) — ND ND ND ND ND ND METHANOL (ppm) — ND ND ND ND ND ND THC (ppm) — 7.5 7 7.5 8 7 8 AMMONIA (ppm) — 230 ND ND 600 10 ND NO_(x) (ppm) — 0.5 6 5 0.5 15 23 NO₂ (ppm) — ND ND ND ND ND 17 CO (ppm) — ND ND ND 2 ND ND CO₂ (ppm) — 7100 7400 7600 7100 7500 7600

[0084] Even when any one of the catalysts “1” and “2” was used, trimethylamine or methanol, which can be produced by decomposition of tetramethylammonium hydroxide, was not detected.

[0085] It is found that, in the case of tratment at a temperature of 325° C. or more, TOC was decreased, carbon monoxide was not detected, and most of carbon component was converted into carbon dioxide. Furthermore, even in connection with nitrogen component, it is found that the concentration of ammonia produced was decreased, NO_(x) was detected in a very small amount, and thus most of them was converted into nitrogen gas.

[0086] Additionally, waste water was continuously treated with the catalyst “1” under conditions mentioned above for 600 hours. We found that the efficiency of treatment did not decrease, and that Si, S and Al included in waste water were removed with a pre-treating agent, and that the function of catalysts in the reactor was not damaged.

[0087] This application is based on Japanese application no. 2000-114086 filed in Japan on Apr. 14, 2000, the contents of which are hereby incorporated by reference.

[0088] Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein. 

What is claimed is:
 1. A method of treating waste water, comprising: a first step of spraying waste water including a nitrogen-containing organic compound in a heated space to gasify substantially all amount of said waste water to waste gas; and a second step of oxidizing said waste gas by contacting with a catalyst to convert said nitrogen-containing organic compound into nitrogen gas, carbon dioxide and water vapor.
 2. A method of treating waste water according to claim 1 , wherein said first step is carried out by heating said space to a temperature of 100° C. or more.
 3. A method of treating waste water according to claim 1 , wherein said catalyst comprises: the component “A” of an oxide including titania and/or titania-silica; the component “B” of an oxide of at least one metal selected from the group consisting of vanadium, tungsten, molybdenum, cerium and iron; and the component “C” of at least one metal selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, manganese, chromium and copper, or an oxide thereof.
 4. A method of treating waste water according to claim 1 , wherein said second step is carried out by flowing said waste gas at a space velocity of 500 to 50000 per hour at a temperature of 100° to 400° C.
 5. A method of treating waste water according to claim 1 , wherein said second step is carried out, after a solid material not gasified in the first step is removed.
 6. A method of treating waste water according to claim 1 , wherein said nitrogen-containing organic compound comprises tetraalkylammonium hydroxide.
 7. A method of treating waste water according to claim 1 , wherein said waste water contains a dissolved component from a resist material.
 8. An apparatus for treating waste water, comprising: a means for gasifying waste water, which includes a sprayer for spraying waste water; a gasifying area in to which waste water is introduced, and in which said waste water is gasified by said gasifying means to produce a waste gas from said waste water; a reaction area which contains a catalyst for oxidizing said waste gas delivered from said gasifying area, and from which an oxidized gas is exhausted; and a line connecting said gasifying area to said reaction area.
 9. An apparatus for treating waste water according to claim 8 , further comprises a pretreatment area for removing a solid material not gasified in said gasifying area.
 10. An apparatus for treating waste water according to claim 9 , wherein said pretreatment area contains at least one selected f rom the group consisting of alumina, silica, titania and zirconia.
 11. An apparatus for treating waste water according to claims 8, wherein said catalyst comprises: the component “A” of an oxide including titania and/or titania-silica; the component “B” of an oxide of at least one metal selected from the group consisting of vanadium, tungsten, molybdenum, cerium and iron; and the component “C” of at least one metal selected from the group consisting of platinum, palladium, iridium, rhodium, ruthenium, manganese, chromium and copper, or an oxide thereof.
 12. An apparatus for treating waste water according to claim 8 , wherein said gasifying means includes a heater.
 13. An apparatus for treating waste water according to claim 8 , wherein said gasifying means utilizes heat exchange between said waste water and a gas discharged from said reaction area. 